A study on application of artificial neural networks(ANN) to active structural control is presented. A feedforward neural network with an adaptive back propagation training method is used in this paper. In the back propagation training, the learning rate is determined by ensuring the decrease of the total error function of the output training patterns at each training cycle. Four-layer-BP networks is constructed to produce the active force for the building structure subjected to earthquake excitation. Numerical examples of single-degree-of freedom systems under earthquake excitations are given to illustrate the effectiveness of the proposed control strategy.